Optical exposure method

ABSTRACT

An optical exposure method in photolithography applied for precise processing when semiconductor devices are produced. A pattern on a photomask is projected and exposed on a register on a base plate with an exposure device including a deformation illumination system, a photomask and a projection lens. The deformation illumination system is composed of a light source, a diaphragm and a condenser lens, and the diaphragm is provided with a linear through-hole. The optical exposure method uses a ray of linear light for illumination or two rays of linear light for illumination that are parallel with the pattern. The two rays of linear light are symmetrical with respect to an optical axis. These rays are parallel with the pattern in a position separate from the optical axis of the exposure device when the photomask pattern is a line and space pattern.

This application is a divisional application under 37 C.F.R. §1.53(b) ofprior application Ser. No. 08/734,790 filed Oct. 25, 1996 which is adivisional application of application Ser. No. 08/510,128, filed Aug. 1,1995, now U.S. Pat. No. 5,607,821, which is a divisional application ofapplication Ser. No. 08/069,853 filed Jun. 1, 1993, now U.S. Pat. No.5,465,220.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to photolithography which is applied forprecise processing when semiconductor devices are produced, and moreparticularly relates to an optical exposure method used forphotolithography.

When semiconductor devices such as ultra-LSIs are highly integrated andprecise processing is required, manufacturers greatly rely onimprovements in lithographic technology. Photolithography using light issuitable for mass production. Therefore, it is adopted for economicalreasons.

2. Description of the Related Art

In order to improve resolution in optical exposure technology, it isimportant to increase the numerical aperture (NA) and to reduce thewavelength of light generated by a light source. On the other hand, thefocal depth is reduced as NA is increased. Recently, attention has beengiven to a deformation illumination method (an oblique incidentillumination method) which improves the critical resolution and focaldepth (for example, shown in pages 28-37 of “Nikkei Micro Device” No.82, April, 1992).

For holes in the diaphragm (the apertures) in the deformationillumination method, zonal holes and four holes symmetrical with respectto a point are well known. In a conventional illumination method, a rayof illumination light sent from a circular hole, coinciding with anoptical axis, to a photomask (reticule) is vertically incident and animage is formed by three beams of light of 0, +1, and −1. However, withthis deformation illumination method, the position of the diaphragm isshifted from the optical axis, so that illumination light sent from thehole is obliquely incident on the photomask, and image formation isconducted by two beams of light of 0 and +1 sent from the photomask. Ina focal position, higher contrast can be provided by the conventionalillumination method, however, in a defocal position, higher contrast canbe provided by the deformation illumination method, so that the focaldepth and resolution can be considerably improved.

In the conventional deformation illumination method, i.e., only for asimple line and space pattern, a pattern of the photomask is projectedand exposed on a register with a diaphragm having the aforementionedgeneral type of diaphragm holes. Accordingly, the illumination systemdoes not meet the requirement of each pattern, so that the effect ofoblique incidence of the deformation illumination method is notsufficient.

Also, recently, attention has been given a lithographic technology usinga phase shift mask, and the following pattern forming method has beenreported to be an effective technology: an unexposed portion (pattern)is used that is accompanied by a sharp decrease of optical intensitygenerated by a step portion (the phase of exposure light is changed by180° by this step portion) of a phase shifter of a phase shift mask.

However, when a pattern is formed by this technology, the unexposedportion (pattern) is formed in all step portions of the phase shifter.Therefore, in many applicable fields, it is necessary to provide aprocess to inhibit the formation of a pattern generated by the unexposedportion generated by an unnecessary step portion of the phase shifter.

Therefore, the following techniques have been conventionally proposed toease the sharp decrease of optical intensity: another exposure mask isput on the unnecessary unexposed portion so as to conduct an exposureoperation (double exposure); and a multi-shifter (step of 90°) isprovided stepwise in a step portion of the phase shifter, the patternformation of which is not necessary.

However, in the double exposure method that has been conventionallyproposed as a method to remove an unnecessary unexposed portion, it isnecessary to manufacture a plurality of masks so as to conductmulti-exposures. Accordingly, it is necessary to increase the number ofthe mask manufacturing processes. On the other hand, it is alsonecessary to ensure an alignment of the double exposure, so that thethroughput is lowered.

Moreover, when a multi-shifter is manufactured, a complicated anddifficult process technique is required in order to provide an opticallyaccurate multi-shifter, and further a big problem is caused when amanufactured phase shift is inspected and corrected.

In order to meet the demand of forming minute patterns, for example,attention is given to an oblique incidence illumination method disclosedin the official gazette of Japanese Unexamined Patent Publication No.2-142111 (1990). According to this method, a ray of light that isvertically incident on a lens is incident being oblique at apredetermined angle, so that focusing is conducted using interference oflight.

However, in the aforementioned conventional method, the-same lightsource is used for any device patterns without giving attention to theprofile of the light source. Accordingly, problems are caused.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a projectionexposure method with a deformation illumination system optimal for adevice pattern (photomask pattern).

It is another object of the present invention to provide a method bywhich an unnecessary unexposed portion can be easily removed withoutusing the aforementioned multi-exposure method or relying on thetechnique in which the phase shift mask having a multi-shifter is used,in the case where a pattern is formed using the unexposed portionaccompanied by a sharp decrease of optical intensity caused by a stepportion of the phase shifter.

It is another object of the present invention to provide an optimizationmethod for a light source profile to obtain an optimal light sourceprofile in accordance with a device pattern.

It is another object of the present invention to realize an opticalprojection exposure in which resolving power can be provided that ishigher than that of the conventional phase shift mask or obliqueincidence illumination.

The aforementioned object can be accomplished by an optical exposuremethod by which a pattern on a photomask is projected and exposed on aregister on a base plate with an exposure device including a deformationillumination system composed of a light source, a diaphragm and acondenser lens, and also including a photomask and a projection lens,wherein the optical exposure method uses a ray of linear light forillumination that is parallel with a photomask pattern in a positionseparate from an optical axis of the exposure device (or the opticalexposure method uses two rays of linear light for illumination that aresymmetrical with respect to the optical axis) when the photomask patternis a line and space pattern.

The aforementioned object can be accomplished by an optical exposuremethod, wherein the optical exposure method uses a ray of first linearlight for illumination that is parallel with a first pattern portion ina position separate from the optical axis of the exposure system (or theoptical exposure method uses two rays of first linear light forillumination that are parallel with the first pattern portionsymmetrical with respect to the optical axis), the optical exposuremethod also uses a ray of second linear light for illumination that isparallel with a second pattern portion in a position separate from theoptical axis of the exposure system (or the optical exposure method alsouses two rays of second linear light for illumination that are parallelwith the second pattern, two rays of second linear light beingsymmetrical with respect to the optical axis), when the first patternportion of line and space, and the second pattern portion of similarline and space make a right angle with each other in the photomaskpattern.

Moreover, it is preferable to use an optical exposure method in whichthe first linear light and the second linear light are oblique by anangle φ with respect to the optical axis in a position on the photomask,and an equation 2p·sin φ=λ is satisfied (where p is a setting pitch ofthe line and space pattern on the projection surface, and λ is awavelength of light).

The object of the present invention can be accomplished by an opticalexposure method by which a pattern on a photomask is projected andexposed on a register on a base plate with an exposure device includinga deformation illumination system composed of a light source, adiaphragm and a condenser lens, and also including a photomask and aprojection lens, wherein the optical exposure method uses a ray of firstblock light for illumination that is parallel with the bottom surface ofthe triangular wave in a position separate from the optical axis of theexposure device (or the optical exposure method uses two rays of firstblock light for illumination that are symmetrical with respect to theoptical axis and parallel with the bottom surface of the triangularwave), and the optical exposure method also uses a ray of second blocklight for illumination that is perpendicular to the bottom surface ofthe triangular wave (or the optical exposure method also uses two raysof second block light for illumination that are symmetrical with respectto the optical axis and perpendicular to the bottom surface of thetriangular wave), when the photomask pattern is a line and space patternof a triangular shape, the bottom angle of which is θ.

Moreover, it is preferable to adopt an optical exposure method in whichthe optical exposure method characterized in that: the first block lightis oblique by an angle φ_(x) with respect to the optical axis in aposition on the photomask, an equation 2p·sin φ_(x)=λ sin θ beingsatisfied (p is a setting pitch of line and space pattern in a register,and λ is a wavelength of light); the second block light is oblique by anangle φ_(y) with respect to the optical axis in a position on thephotomask, an equation 2p·sin φ_(y)=λ cos θ being satisfied; and a ratioof the illumination area of the first block light to that of the secondblock light is sin θ:cos θ.

In the optical exposure method of the present invention, the mostappropriate illumination light shape and oblique incident angle φ areset in accordance with each photomask pattern, so that the resolutionand focal depth and improved for each pattern. Especially when the pitchof line and space of a photomask pattern is close to 1:1, the opticalexposure method of the invention is especially effective. In thisconnection, a pattern of line and space corresponds to a plurality oflinear shading (or transmission) stripes of a photomask that aredisposed in parallel at regular intervals on a developed registerpattern.

In the aforementioned equation 2p·sin φ=λ, wavelength λ becomes constantfor g ray (434 nm), i ray (365 nm) or excimer laser beam (254 nm for KeFexcimer laser beam), and incident angle φ is determined in accordancewith pattern pitch width p.

According to another aspect of the present invention, there is provideda projection exposure method of the present invention comprising thesteps of: irradiating an exposure mask with exposing light having anoptical intensity distribution extending in a primary direction in itssection; and projecting the light transmitted through the exposure maskon a surface to be exposed, wherein exposure is carried out withexposure characteristics relying on a direction of the mask pattern ofthe exposure mask.

Moreover, the present invention is to provide a projection exposuremethod comprising the steps of: irradiating a phase shift exposure maskwith exposing light having an optical intensity distribution extendingin a primary direction in its section; and projecting the lighttransmitted through the phase shift exposure mask on a surface to beexposed, wherein exposure is carried out with exposure characteristicsrelying on a direction of the mask pattern of the phase shift exposuremask. Especially, an exposing process is adopted in which exposure iscarried out with non-symmetrical exposure characteristics including onedirection of a step in which an unexposed portion is formed having asharp decrease of optical intensity caused close to an edge portion ofthe phase shifter of the phase shift exposure mask, and also includingthe otter direction of a step in which an unexposed portion is notformed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exposure device of deformationillumination (oblique incidence illumination);

FIG. 2 is a partial plan view of a pattern of line and space;

FIG. 3 is a plan view of a diaphragm provided with two linearthrough-holes;

FIGS. 4(a)-4(d) are a set of graphs showing the optical intensity inperpendicular directions in accordance with the pattern of FIG. 2 on aprojection surface when the diaphragm of FIG. 3 is used. FIG. 4(a) is agraph showing the optical intensity in the case where an image is infocus, FIG. 4(b) is a graph showing the optical intensity in the casewhere an image is out of focus, wherein the focus slippage is 0.5 μm,FIG. 4(c) is a graph showing the optical intensity in the case where animage is out of focus, wherein the focus slippage is 1.0 μm, and FIG.4(d) is a graph showing the optical intensity in the case where an imageis out of focus, wherein the focus slippage is 1.5 μm;

FIGS. 5(a)-5(d) are a set of graphs showing the optical intensity inperpendicular directions on projection surfaces in accordance with thepattern of FIG. 2 when a conventional circular hole diaphragm is used.FIG. 5(a) is a graph showing the optical intensity in the case where animage is in focus, FIG. 5(b) is a graph showing the optical intensity inthe case where an image is out of focus, wherein the focus slippage is0.5 μm, FIG. 5(c) is a graph showing the optical intensity in the casewhere an image is out of focus, wherein the focus slippage is 1.0 μm,and FIG. 5(d) is a graph showing the optical intensity in the case wherean image is out of focus, wherein the focus slippage is 1.5 μm;

FIG. 6 is a plan view of a diaphragm provided with one linearthrough-hole;

FIG. 7 is a partial plan view of a combination pattern in which a pairof patterns are combined, wherein the patterns make a right angle witheach other;

FIG. 8 is a plan view of a diaphragm provided with two pairs of parallellinear through-holes, wherein the pairs of parallel linear through-holesmake a right angle with each other;

FIGS. 9(a)-9(f) are a set of graphs showing three dimensional opticalintensity distributions on the projection surface in accordance with thepattern of FIG. 7 when the diaphragm of FIG. 8 is used. In FIG. 9(a),the optical intensity distribution is shown in the case of imageformation conducted in a focal position (in focus). In FIG. 9(b), theoptical intensity distribution is shown in the case of image formationconducted out of focus, wherein the amount of focus slippage is 0.2 μm.In FIG. 9(c), the optical intensity distribution is shown in the case ofimage formation conducted out of focus, wherein the amount of focusslippage in 0.4 μm. In FIG. 9(d), the optical intensity distribution isshown in the case of image formation conducted out of focus, wherein theamount of focus slippage is 0.6 μm. In FIG. 9(e), the optical intensitydistribution is shown in the case of image formation conducted in aposition out of focus, wherein an amount of focus slippage is 0.8 μm. InFIG. 9(f), the optical intensity distribution is shown in the case ofimage formation conducted out of focus, wherein the amount of focusslippage is 1.0 μm;

FIGS. 10(a)-10(f) are a set of graphs showing three dimensional opticalintensity distributions on the projection surface in accordance with thepattern of FIG. 7 when a conventional circular diaphragm is used. FIG.10(a) is a graph showing the optical intensity distribution in the caseof image formation conducted in a focal position (in focus). FIG. 10(b)is a graph showing the optical intensity distribution in the case ofimage formation conducted out of focus, wherein the amount of focusslippage is 0.2 μm. FIG. 10(c) is a graph showing the optical intensitydistribution in the case of image formation conducted out of focus,wherein the amount of out of focus is 0.4 μm. FIG. 10(d) is a graphshowing the optical intensity distribution in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.6 μm. FIG. 10(e) is a graph showing the optical intensitydistribution in the case of image formation conducted in a position outof focus, wherein an amount of focus slippage is 0.8 μm. FIG. 10(f) is agraph showing the optical intensity distribution in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 1.0 μm;

FIG. 11 is a plan view of a diaphragm provided with linear through-holesmaking a right angle with each other;

FIG. 12 is a partial plan view of a triangular wave line and spacepattern;

FIG. 13 is a plan view of a diaphragm provided with two pairs blockthrough-holes, wherein each pair includes two block through-holesseparate from an optical axis;

FIG. 14 is a partial plan view of a triangular wave line and spacepattern utilized in a DRAM activation region;

FIG. 15 is a plan view of a diaphragm provided with two pairsrectangular through-holes, wherein each pair includes two rectangularthrough-holes separate from an optical axis;

FIGS. 16(a)-16(c) are a set of graphs showing three dimensional opticalintensity distributions on a projection surface in accordance with thepattern of FIG. 14 when the diaphragm of FIG. 15 is utilized. FIG. 16(a)is a graph showing the optical intensity distribution in the case ofimage formation conducted in a focal position (in focus). FIG. 16(b) isa graph showing the optical intensity distribution in the case of. imageformation conducted out of focus, wherein the amount of focus slippageis 0.2 μm. FIG. 16(c) is a graph showing the optical intensitydistribution in the case of image formation conducted out of focus,wherein the amount of focus slippage is 0.4 μm;

FIGS. 17(a)-17(d) are a set of graphs showing three dimensional opticalintensity distributions on a projection surface in accordance with thepattern of FIG. 14 when the diaphragm of FIG. 15 is used. FIG. 17(a) isa graph showing the optical intensity distribution in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.6 μm. FIG. 17(b) is a graph showing the optical intensitydistribution in the case of image formation conducted in a position outof focus, wherein an amount of focus slippage is 0.8 μm. FIG. 17(c) is agraph showing the optical intensity distribution in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 1.0 μm. FIG. 17(d) is a graph showing the optical intensitydistribution in the case of image formation conducted out of focus,wherein the amount of focus slippage is 1.2 μm;

FIG. 18 is a plan view of a diaphragm provided with a through-holecorresponding to a conventional circular hole;

FIGS. 19(a)-19(c) are a set of graphs showing three dimensional opticalintensity distributions on a projection surface in accordance with thepattern of FIG. 14 when the conventional diaphragm of FIG. 19 is used.FIG. 19(a) is a graph showing the optical intensity distribution in thecase of image formation conducted in a focal position. FIG. 19(b) is agraph showing the optical intensity distribution in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.2 μm. FIG. 19(c) is a graph showing the optical intensitydistribution in the case of image formation conducted out of focus,wherein the amount of focus slippage is 0.4 μm;

FIGS. 20(a)-20(d) are a set of graphs showing three dimensional opticalintensity distributions on a projection surface in accordance with thepattern of FIG. 14 when the conventional diaphragm of FIG. 19 is used.FIG. 20(a) is a graph showing the optical intensity distribution in thecase of image formation conducted out of focus, wherein the amount offocus slippage is 0.6 μm. FIG. 20(b) is a graph showing the opticalintensity distribution in the case of image formation conducted out offocus, wherein the amount of focus slippage is 0.8 μpm. FIG. 20(c) is agraph showing the optical intensity distribution in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 1.0 μm. FIG. 20(d) is a graph showing the optical intensitydistribution in the case of image formation conducted out of focus,wherein the amount of focus slippage is 1.2 μm;

FIG. 21 is a plan view showing a diaphragm provided with two sets ofblock through-holes separate from an optical axis;

FIG. 22 is a sectional view schematic of a fly-eye lens and a liquidcrystal plate diaphragm;

FIG. 23 is a schematic illustration of an optical projection exposuredevice of deformation illumination system;

FIG. 24 is a plan view of a deformation illumination diaphragm providedwith 4 holes;

FIG. 25 is a partial plan view of a line pattern of a photomask;

FIG. 26 is a partial plan view of a register line pattern provided by aconventional optical projection exposure device;

FIG. 27 is a partial plan view of a register line pattern in thedeformation illumination system;

FIG. 28 is a schematic illustration showing a relation between aphotomask and a diaphragm in the case of incident light of threedirections in the deformation illumination system;

FIG. 29 is a schematic illustration showing a relation between aphotomask and a diaphragm in the case of incident light of twodirections (in the case of excellent resolution) in the deformationillumination system;

FIG. 30 is a partial plan view schematic of a pattern in a DRAM (dynamicrandom access memory);

FIG. 31 is partial plan view schematic of a pattern in an activationregion of a DRAM;

FIG. 32 is a plan view showing a configuration of common illumination;

FIG. 33 is a plan view showing a configuration of division illumination;

FIGS. 34(a) and 34(b) are plan views showing the rotation of divisionillumination in the case where they do not make a right angle with eachother;

FIG. 35 is a schematic illustration showing the structure of aprojection exposure device used for the projection exposure method;

FIGS. 36(a) and 36(b) are schematic illustrations of the diaphragm ofthe projection exposure device used for the projection exposure method;

FIG. 37 is an optical intensity distribution diagram of exposure lighttransmitted through the phase shifter step portion parallel with theprimary direction of the exposure light;

FIG. 38 is an optical intensity distribution diagram of exposure lighttransmitted through the phase shifter step portion perpendicular to theprimary direction of the exposure light;

FIGS. 39(a) and 39(b) are schematic illustrations of the projectionexposure method of the embodiment 8;

FIGS. 40(a) and 40(b) are schematic views of a pattern showing theeffect of the embodiment 8;

FIGS. 41(a) and 41(b) are schematic illustrations of the projectionexposure method of the embodiment 9;

FIG. 42 is a schematic illustration of the projection exposure method ofthe embodiment 10;

FIGS. 43(a) to 43(c) are schematic illustrations of the projectionexposure method of the embodiment 11;

FIG. 44 is a schematic illustration of the projection exposure method ofthe embodiment 12;

FIG. 45 is a view showing the principle of the optimization method for alight source profile of the embodiment 13;

FIG. 46 is a flow chart showing an outline of processing of theembodiment 13;

FIG. 47 is a flow chart showing primary processing of the embodiment 13;

FIG. 48 is a view showing an example of the optimized light sourceprofile of the embodiment 13;

FIG. 49 is a view showing an example of the optimized light sourceprofile of the embodiment 13;

FIGS. 50(a)-50(f) are is a set of views showing pattern images for eachfocal position obtained by the light source shown in FIG. 48;

FIGS. 51(a)-51(f) are is a set of views showing pattern images for eachfocal position obtained by the light source shown in FIG. 49;

FIG. 52 is a flow chart showing primary processing of the embodiment 14;

FIGS. 53(a) and 53(b) are views showing examples of mask patterns;

FIGS. 54(a)-54(c) are is a set of views showing spectral distributionsof the pattern shown in FIG. 53(a);

FIGS. 55(a)-55(c) are is a set of views showing spectral distributionsof the pattern shown in FIG. 53(b);

FIG. 56 is a view showing examples of a conventional light sourceprofile;

FIGS. 57(a)-57(f) are is a set of views showing pattern images for eachfocal position obtained by the light source shown in FIG. 56;

FIGS. 58(a)-58(f) are a set of views showing pattern images for eachfocal position obtained by the light source shown in FIG. 56;

FIG. 59 is a perspective view for explaining an outline of projectionexposure according to the embodiment 15;

FIG. 60 is a schematic illustration showing a profile of an experimentalpattern of exposure of the embodiment shown in FIG. 59;

FIGS. 61(a) and 61(b) are schematic views showing experimental results;

FIG. 62 is a perspective view for explaining projection exposure of theembodiment 16;

FIGS. 63(a)-63(d) are a set of schematic illustrations for explaining aexposure technique in which the phase difference is utilized;

FIGS. 64(a) and 64(b) are a pair of diagrams showing an outline of aphase shift mask;

FIGS. 65(a) and 65(b) are a pair of diagrams showing an outline ofoblique incidence illumination exposure; and

FIGS. 66(a) and 66(b) are a pair of diagrams showing an outline of thedifference of image formation capacity caused by polarization.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 22, the first aspect of the presentinvention will now be explained in detail with embodiments andcomparative examples.

FIG. 1 is a schematic illustration of an exposure device (stepper). Theexposure device comprises: a deformation illumination system 4 includinga light source 1 composed of a mercury lamp (excimer laser), a diaphragm2 provided with a through-hole, and a condenser lens 3; a photomask(reticule) 5 having a predetermined pattern; a projection lens 6; and aregister film (projection surface) 7 coated on a base plate. Thisstructure is the same as that of a conventional exposure device, andonly a configuration of the through-hole of the diaphragm 2 is differentfrom that of the conventional exposure device. In this connection, acompound eye condenser lens (fly eye lens) may be provided between thelight source 1 and the diaphragm 2 in the same manner as theconventional exposure device.

In this embodiment, the configuration of the light source is determinedby the configuration of the diaphragm through-hole. However, theindividual single eyes may be disposed to be a target configuration ofthe light source using a fly eye lens. In order to change the lightsource configuration in accordance with the object of use, in the casewhere a diaphragm is used, the diaphragm may be replaced with anotherone having a through-hole of different configuration. Alternatively, theindividual single eyes 51 a to 51 f of the fly eye lens 51 (FIG. 22) maybe provided with opening and closing function. For example, a liquidcrystal plate 52 is disposed at the exit or entrance of the single eyeof the fly eye lens, and voltage is impressed upon an electrode 53located in a position corresponding to the single eye so that the lightcan be transmitted or not.

Embodiment 1

A line and space pattern 13 composed of opaque stripes 11 andtransmitting stripes 12 shown in FIG. 2 is formed on the photomask 5 bya conventional method. The photomask 5 is made when a chrome shadingfilm of this pattern is provided on a quartz glass plate. Pitch A of theline and space corresponds to setting pitch p of the register pattern tobe obtained. In order to provide illumination of the present invention,as shown in FIG. 3, two linear through-holes (or light transmissionapertures) 16 are formed in the diaphragm 15 in parallel with eachother, wherein the two linear through-holes 16 are disposedsymmetrically with respect to an optical axis of the exposure device.Consequently, two slits are formed in the shading diaphragm, so that thelight emitted from the light source 1 passes through these slits and isincident on the condenser lens 3. In this connection, the diaphragm 15is disposed so that these linear through-holes 16 can be in parallelwith the line and space pattern 13 of the photomask. Then, the photomask5 is illuminated with light sent from the condenser lens 3, wherein theincident angle of light is φ. In this case, the incident angle is anangle formed between the light and the optical axis of the exposuredevice in a position on the photomask. Next, the diffraction light of 0and +1 orders sent from the photomask 5 is projected on the projectionlens 6, and the diffraction light is collected by the lens, so that apattern image is formed on the register film 7 on the projectionsurface. The pattern 13 of the photomask 5 is projected and exposed onthe register film 7 on a base plate of a semiconductor wafer, and thenthe projected image is developed so as to obtain a register pattern.

In the case where optical exposure was conducted under the followingconditions, optical intensity in a direction perpendicular to the lineand space pattern is shown in FIGS. 4(a) to 4(d), wherein the projectionsurface of the register film is located in a focal position of theprojection lens or in a position shifted from the focal position(defocus).

Wavelength (λ) of light source i ray (0.365 μm) Numerical aperture oflens (NA) 0.5 Coherence factor (σ) 0.5 Setting pitch (p) of line andspace 0.35 μm Incident angle (φ) 31.4° (calculated from 2 × 0.35 × sin φ= 0.365)

In FIG. 4(a), the optical intensity is shown in the case of imageformation conducted in a focal position (in focus). In FIG. 4(b), theoptical intensity is shown in the case of image formation conducted outof focus, wherein the amount of defocus is 0.5 μm. In FIG. 4(c), theoptical intensity is shown in the case of image formation conducted outof focus, wherein the amount of defocus is 1.0 μm. In FIG. 4(d), theoptical intensity is shown in the case of image formation conducted outof focus, wherein the amount of defocus is 1.5 μm. As can be seen inFIGS. 4(a) to 4(d), the profiles of optical intensity are approximatelythe same, and the focal depth is large.

As a comparative example, optical exposure was conducted with the sameoptical exposure device using a conventional circular diaphragm (σ=0.5).The optical intensity on the projection surface on the register film inthe focal and non-focal positions are shown in FIGS. 5(a) to (d).

In FIG. 5(a), the optical intensity is shown in the case of imageformation conducted in a focal position (in focus). In FIG. 5(b), theoptical intensity is shown in the case of image formation conducted outof focus, wherein the amount of focus slippage is 0.5 μm. In FIG. 5(c),the optical intensity is shown in the case of image formation conductedout of focus, wherein the amount of focus slippage is 1.0 μm. In FIG.5(d), the optical intensity is shown in the case of image formationconducted out of focus, wherein the amount of focus slippage is 1.5 μm.As can be seen in FIGS. 5(a) to 5(d), concerning the profile of opticalintensity, the larger the amount of focal slippage is, the smaller thecontrast of optical intensity becomes, so that the resolution isdeteriorated. Naturally, the focal depth is smaller than that of thedevice of the present invention.

Embodiment 2

In the above-mentioned embodiment, the optical exposure device and thephotomask 5 of embodiment 1 were used. In the embodiment 2, thediaphragm was replaced with a diaphragm 17 shown in FIG. 6, wherein thenumber of the linear through-holes 16 was one. The diaphragm 17 wasdisposed so that the linear through-hole 16 could be parallel with thepattern 13 of the line and space of the photomask. In this case, thelight emitted from the light source 1 passed through the linearthrough-hole 16, and was incident on the condenser lens 3, so that thephotomask 5 was illuminated with the light, the incident angle of whichwas φ. Next, the diffraction light of 0 and +1 orders sent from thephotomask 5 was projected on the projection lens 6, and the diffractionlight was collected by the lens, so that a pattern image was formed onthe register film 7 on the projection surface. The pattern 13 of thephotomask 5 was projected and exposed on the register film 7, and thenthe projected image was developed so as to obtain a register pattern. Inthe case of embodiment 1, the photomask was illuminated with light fromboth the right and left, however, in the case of embodiment 2, thephotomask was illuminated with light in one direction. Therefore, ascompared with the results of embodiment 1, the pattern profile was moredeteriorated by the slippage of focus. However, as compared with theaforementioned comparative example, the focal depth was large andresolution was high.

Embodiment 3

A pattern 23 was formed on the photomask 5 by a well known method asshown in FIG. 7, wherein the pattern 23 was composed of a square shadingregion 21 in which squares were cyclically disposed at regularintervals, and a through-hole region 22 surrounding the square shadingregion 21. In this pattern 23, the line and space pattern shown in FIG.2 and the same line and space pattern disposed perpendicular to it arecombined. Pitch A of the line and space (the interval of the width ofthe shading region 21) corresponds to setting pitch p of the line andspace of the register pattern to be obtained. In order to provideillumination of the present invention, as shown in FIG. 8, two linearthrough-holes 25, which are the same as those of embodiment 1, areformed in the diaphragm 24 in parallel with each other, wherein the twolinear through-holes 25 are disposed symmetrically with respect to anoptical axis of the optical exposure device. Moreover, two linearthrough-holes 26 perpendicular to these linear through-holes 25 aredisposed in parallel with each other symmetrically with the opticalaxis. The two linear through-holes 25 compose the first linear light,and another pair of linear through-holes 26 compose the second linearlight, and these two pairs of through-holes 25 and 26 are disposed inthe same position when one of them is rotated around the optical axis byangle 90°. Accordingly, four slits are formed in the shading diaphragm,and the light emitted from the light source 1 passes through these slitsand is incident on the condenser lens 3. In this connection, thediaphragm 24 is disposed so that these linear through-holes 25 and 26can be in parallel with the line and space pattern 23 of the photomask.Then, the photomask 5 is illuminated with light sent from the condenserlens 3, wherein the incident angle of light is φ. In this case, theincident angle is an angle formed between the light and the optical axisof the exposure device in a position on the photomask. Next, thediffraction light of 0 and +1 orders sent from the photomask 5 isprojected on the projection lens 6, and the diffraction light iscollected by the lens, so that a pattern image is formed on the registerfilm 7 on the projection surface. The pattern 23 of the photomask 5 isprojected and exposed on the register film 7 on a base plate of asemiconductor wafer, and then the projected image is developed so as toobtain a register pattern.

An exposure simulation was carried out with the exposure device ofembodiment 1 under the following conditions, wherein the projectionsurface of the. register film was disposed in a focal position of theprojection lens and also disposed in a position out of focus. The threedimensional optical intensity distribution is shown in FIGS. 9(a) to9(f) illustrated with equal intensity lines.

Wavelength (λ) of light source i ray (0.365 μm) Numerical aperture oflens (NA) 0.5 Coherence factor (σ) 0.5 Setting pitch (p) of line andspace 0.35 μm Incident angle (φ) 31.4° (calculated from 2 × 0.35 × sin φ= 0.365)

In FIG. 9(a), the optical intensity distribution is shown in the case ofimage formation conducted in a focal position (in focus). In FIG. 9(b),the optical intensity distribution is shown in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.2 μm. In FIG. 9(c), the optical intensity distribution is shown inthe case of image formation conducted out of focus, wherein the amountof focus slippage is 0.4 μm. In FIG. 9(d), the optical intensitydistribution is shown in the case of image formation conducted out offocus, wherein the amount of focus slippage is 0.6 μm. In FIG. 9(e), theoptical intensity distribution is shown in the case of image formationconducted in a position out of focus, wherein an amount of focusslippage is 0.8 μm. In FIG. 9(f), the optical intensity distribution isshown in the case of image formation conducted out of focus, wherein theamount of focus slippage is 1.0 μm. As can be seen in FIGS. 9(a) to (f),the profiles of optical intensity distributions are approximately thesame, and the focal depth is large.

As a comparative example, exposure was conducted with the same exposuredevice using a conventional circular diaphragm (σ=0.5). The opticalintensity distribution on the projection surface on the register film inthe focal and non-focal positions are shown in FIGS. 10(a) to (f).

In FIG. 10(a), the optical intensity distribution is shown in the caseof image formation conducted in a focal position (in focus). In FIG.10(b), the optical intensity distribution is shown in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.2 μm. In FIG. 10(c), the optical intensity distribution is shown inthe case of image formation conducted out of focus, wherein the amountof focus slippage is 0.4 μm. In FIG. 10(d), the optical intensitydistribution is shown in the case of image formation conducted out offocus, wherein the amount of focus slippage is 0.6 μm. In FIG. 10(e),the optical intensity distribution is shown in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.8 μm. In FIG. 10(f), the optical intensity distribution is shown inthe case of image formation conducted out of focus, wherein the amountof focus slippage is 1.0 μm. As can be seen in FIGS. 10(a) to 10(f), themore the focus slippage is increased, the more gentle the difference ofoptical intensity distribution becomes, and the distribution spreads tothe non-exposure portion, so that the contrast of optical intensitydistribution is reduced and the resolution is deteriorated. Naturally,the focal depth is smaller than that of the device of the presentinvention.

Embodiment 4

In this embodiment, the optical exposure device and the photomask 5 ofembodiment 3 were used, but the diaphragm was replaced with a diaphragm27 shown in FIG. 11, wherein the number of the linear through-holes 25and 26 was two. The diaphragm 27 was disposed so that the linearthrough-holes 25 and 26, which made a right angle with each other, couldbe disposed in parallel with the pattern 23 of the square shading region21 on the photomask in which squares were cyclically disposed at regularintervals. In this case, the light emitted from the light source 1passed through the linear through-holes 25 and 26, and was incident onthe condenser lens 3, so that the photomask 5 was illuminated with thelight, the incident angle of which was φ. Next, the diffraction light of0 and +1 orders sent from the photomask 5 is projected on the projectionlens 6, and the diffraction light is collected by the lens, so that apattern image is formed on the register film 7 on the projectionsurface. The pattern 13 of the photomask 5 is projected and exposed onthe register film 7, and then the projected image is developed so as toobtain a register pattern. In the case of. embodiment 3, the photomaskwas illuminated with light from both the right and left, however, in thecase of embodiment 4, the photomask was illuminated with light in onedirection. Therefore, as compared with the results of embodiment 3, thepattern profile was more deteriorated by the slippage of focus. However,as compared with the aforementioned comparative example, the focal depthis large and the resolution is high.

In embodiments 1 to 4, a ray of light passes through a linearthrough-hole in which the width of the slit is selected from 5 to 10 mm.Therefore, when the slit is too narrow, an amount of light (that is, σ)is reduced so that the exposure time is extended. When the slit is toowide, noise components pass through the slit, so that sufficient effectcannot be provided. Preferably, the slit is 5 to 10 mm wide.

Embodiment 5

A pattern 33 of line and space composed of shading stripes 31, thebottom angle of which is φ as shown in FIG. 12, and also composed ofthrough-hole stripes 32, is formed on the photomask 5 by a well knownmethod. Pitch A of the line and space corresponds to setting pitch p ofthe line and space of a register pattern to be obtained. In order toprovide illumination of the present invention, as shown in FIG. 13, thefirst block through-holes 35 of the same configuration as the diaphragm34, the number of which is two, are formed in a position separate fromthe optical axis of the exposure device, wherein the first blockthrough-holes 35 are disposed in parallel with the longitudinaldirection of the stripe symmetrically with respect to the optical axis.Moreover, the second block through-holes 36 of the same configuration,the number of which is two, are formed in a position separate from theoptical axis of the exposure device, wherein the second blockthrough-holes 36 are disposed in parallel with the longitudinaldirection of the stripe symmetrically with respect to the optical axis(that is, four through-holes are provided in total). The two blockthrough-holes 35 compose the first block of light, and another pair ofblock through-holes 36 compose the second block of light. The areas ofthese through-holes are set so that a ratio of the illumination area ofthe first block light to that of the second block light can be sin φ:cosφ. The configuration of each block through-hole is either rectangular,circular, oval, lozenge-shaped or triangular, and the necessarythrough-hole area must be ensured. Accordingly, four through-holes areformed in the shading diaphragm, and a ray of light emitted from thelight source 1 passes through these through-holes, and is incident onthe condenser lens 3. Illumination is conducted on the photomask 5 bythe light passing through the condenser lens 3, wherein the incidentangle of the block through-hole 35 is φ_(x), and the incident angle ofthe block through-hole 35 is φ_(y). In this case, these incident anglesare defined as an angle formed between the ray of light and the opticalaxis of the optical exposure device. Concerning incident angle φ_(x), anequation 2p·sin φ_(x)=sin φ is satisfied (where p is a setting pitch ofthe line and space pattern, and λ is a wavelength of light.) Concerningincident angle φ_(y), an equation 2p·sin φ_(y)=λ cos φ is satisfied.Next, the diffraction light of 0 and +1 orders sent from the photomask 5is projected on the projection lens 6, and the diffraction light iscollected by the lens, so that a pattern image is formed on the registerfilm 7 on the projection surface. The pattern 33 of the photomask 5 isprojected and exposed on the register film 7 on a base plate of asemiconductor wafer, and then the projected image is developed so as toobtain a register pattern.

In the case of a triangular wave stripe-shaped pattern 38 utilized in aDRAM activation region shown in FIG. 14, the photomask blockthrough-holes 39 and 40 shown in FIG. 15 are adopted, and then opticalexposure simulation is carried out under the following conditions. Theprojection surface is set at a focal position and at a position out offocus. In this way, three dimensional optical intensity distributionsexpressed by equal intensity lines are provided that are shown in FIGS.16(a) to 16(c) and FIGS. 17(a) to 17(d).

The conditions of the triangular wave stripe-shaped pattern 38 are asfollows.

Setting pitch (p) of line and space 0.35 μm Bottom angle (θ) oftriangular wave stripe i ray (0.365 μm) Numerical aperture of lens (NA)0.5 Coherence factor (σ) 0.5 Incident angle (φ_(x)) of blockthrough-hole 39 74.8° Incident angle (φ_(y)) of block through-hole 4026.8° Ratio of the area of block through-hole 39 0.5:0.866 and that ofblock-through hole 39

In FIG. 16(a), the optical intensity distribution is shown in the caseof image formation conducted in a focal position (in focus). In FIG.16(b), the optical intensity distribution is shown in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.2 μm. In FIG. 16(c), the optical intensity distribution is shown inthe case of image formation conducted out of focus, wherein the amountof out of focus is 0.4 μm. In FIG. 17(a), the optical intensitydistribution is shown in the case of image formation conducted out offocus, wherein the amount of focus slippage is 0.6 μm. In FIG. 17(b),the optical intensity distribution is shown in the case of imageformation conducted in a position out of focus, wherein an amount offocus slippage is 0.8 μm. In FIG. 17(c), the optical intensitydistribution is shown in the case of image formation conducted out offocus, wherein the amount of focus slippage is 1.0 μm. In FIG. 17(d),the optical intensity distribution is shown in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 1.2 μm. As can be seen in FIGS. 16 and 17, the profiles of opticalintensity distributions are approximately the same when the focalslippage is not more than 1.0 μm, and the focal depth is large.

As a comparative example, optical exposure was conducted with the sameoptical exposure device using a conventional circular diaphragm (σ=0.5)provided with a conventional circular hole 41 shown in FIG. 18. Theoptical intensity distribution on the projection surface in the focaland non-focal positions are shown in FIGS. 19(a) to 19(c) and in FIGS.20(a) to 20(d).

In FIG. 19(a), the optical intensity distribution is shown in the caseof image formation conducted in a focal position (in focus). In FIG.19(b), the optical intensity distribution is shown in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.2 μm. In FIG. 19(c), the optical intensity distribution is shown inthe case of image formation conducted out of focus, wherein the amountof focus slippage is 0.4 μm. In FIG. 20(a), the optical intensitydistribution is shown in the case of image formation conducted out offocus, wherein the amount of focus slippage is 0.6 μm. In FIG. 20(b),the optical intensity distribution is shown in the case of imageformation conducted out of focus, wherein the amount of focus slippageis 0.8 μm. In FIG. 20(c), the optical intensity distribution is shown inthe case of image formation conducted out of focus, wherein the amountof focus slippage is 1.0 μm. In FIG. 20(d), the optical intensitydistribution is shown in the case of image formation conducted out offocus, wherein the amount of focus slippage is 1.2 μm. As can be seen inFIGS. 19 and 20, the more the focus slippage is increased, the moregentle the difference of optical intensity distribution becomes, and thedistribution spreads to the non-exposure portion, so that the contrastof optical intensity distribution is reduced and the resolution isdeteriorated. Naturally, the focal depth is smaller than that of thedevice of the present invention.

Embodiment 6

In this embodiment, the optical exposure device and photomask 5 ofembodiment 5 are used, but the diaphragm is replaced with a diaphragm 45provided with block through-holes 35 and 36 in FIG. 21, each number ofwhich is respectively one. The diaphragm 45 is disposed so that theblock through-hole 35 can be parallel with the bottom surface of thetriangular wave of the triangular wave stripe, and so that the blockthrough-hole 36 can make a right angle with the bottom surface of thetriangular wave. In this case, the light emitted from the light source 1passes through the block through-holes 35 and 36, and is incident on thecondenser lens 3, so that the photomask 5 is illuminated with the light,the incident angle of which is φ_(x) and φ_(y). Next, the diffractionlight of 0 and +1 orders sent from the photomask 5 is projected on theprojection lens 6, and then the diffraction light is collected by thelens, so that a pattern image is formed on the register film 7 on theprojection surface. The pattern 33 of the photomask 5 is projected andexposed on the register film 7, and then the projected image isdeveloped so as to obtain a register pattern. In the case of embodiment5, the photomask was illuminated with light from both the right andleft, however, in the case of embodiment 6, the photomask wasilluminated with light in one direction. Therefore, as compared with theresults of embodiment 5, the pattern profile was more deteriorated bythe slippage of focus. However, as compared with the aforementionedcomparative example, the focal depth is large and resolution is high.

As explained above, according to the optical exposure method of theabove-mentioned embodiments 1-6, the optimal deformation illuminationsystem (configuration of the light source) is adopted in accordance witha pattern to be obtained, and the advantages of oblique incidence(improvements in focal depth and resolution) can be effectivelyutilized, so that the present invention contributes to improve preciselithographic technology.

Referring now to FIGS. 23 through 34, the second aspect of the presentinvention will now be explained in detail with reference to a prior artand the embodiment 7.

Embodiment 7

In FIG. 23, an optical projection exposure device of deformationillumination known in the prior art comprises: an illumination system103 including a light source 135, condenser 136, fly eye lens 101 andillumination lens 102; a photomask 104 provided with a predeterminedpattern 110; a projection lens 105; and a base plate 106 provided with aregister layer, wherein, for example, a diaphragm (referred to as adeformation illumination diaphragm, hereinafter) 107 is disposed betweenthe light source 135 and the photomask 104, and the center of thediaphragm is shaded and through-holes are provided in the positionsseparate from the optical axis. The deformation illumination diaphragm107 is disposed between the light source and the lens 102. As aconfiguration of the hole formed in the deformation illuminationdiaphragm (aperture) 107, zonal holes or four holes 108 (shown in FIG.24) symmetrical with respect to a point are conventionally known.

In the case where a pattern of the photomask 103 is formed, for example,in the case where a pattern shown in FIG. 25 is formed in which avertical portion 111A, horizontal portion 111B and oblique portion 111Care included and in which the line and space is made minute so as to bea value about 0.3 μm, the resolution can not be improved (the resolutionis low) and the aforementioned portions become one heavy register layerline 112 as shown in FIG. 26 when the register layer is exposed anddeveloped by an optical projection exposure method in which aconventional illumination 131 shown in FIG. 32 is used. In the casewhere a register layer on the base plate is exposed by the opticalprojection exposure method of deformation illumination method in whichthe 4 division deformation illumination 133 shown in FIG. 33 is used,and in this time the deformation illumination elements 132 are disposedand developed so that a line connecting two illumination elements, thedistance of which is the shortest, can be parallel or vertical to adirection of the pattern line in the drawing. Then, the parallel andvertical pattern line portions 113A and 113B in the drawing are formedto be a thin register layer line as shown in FIG. 27, however, theoblique pattern line portion 113C is integrated and formed to be a thickregister layer line.

The reason why resolution failure is caused in a portion of the registerpattern as described above is as follows: as shown in FIG. 28, theillumination light (113A, 113B and 113C) incident on the oblique portion111C of the photomask 104 is essentially sent from the elements 132 ofthe deformation illumination 133 in three directions. The reason whyminute resolution can be provided is as follows: as shown in FIG. 29,the illumination light (114A and 114B) incident on the vertical portion111A (or the horizontal portion 111B) of the photomask 104 isessentially sent from the elements 132 of the deformation illumination133 in two directions.

Consequently, as long as the deformation illumination diaphragmincluding 4 holes is fixed, the illumination system is not adapted toeach pattern configuration. Therefore, the effect of oblique incidenceof the deformation illumination method can not be sufficiently exerted.

It is an object of the present invention to provide a projectionexposure method by which exposure is conducted with a deformationillumination system and division illumination system optimal for adevice pattern (photomask pattern) in the case where four divisiondeformation illumination is utilized.

The aforementioned object can be accomplished by an optical projectionexposure method by which a pattern on a photomask is projected andexposed on a register on a base plate with an exposure device includinga deformation illumination system, a photomask and a projection lens,wherein a deformation illumination having four components disposedsymmetrically with respect to an optical axis is used for thedeformation illumination system, and the deformation illumination isrotated so as to conduct exposure in accordance with a direction of aline of the pattern of the photomask.

For each photomask, the deformation illumination is rotated and disposedso that a line to connect two elements located in the shortest distanceamong four elements in the deformation illumination can be parallel orvertical to the line direction of the pattern.

In the present invention, for each pattern, the resolution of which isto be improved, the 4 division deformation illumination is rotatablydisposed so that oblique incident light of two directions can beprovided with respect to the longitudinal direction of the line of thepattern.

Referring to the attached drawings, the present embodiment will beexplained in detail with reference to an embodiment of the presentinvention.

For example, as shown in FIG. 30, a pattern arrangement in a DRAM(dynamic random access memory) includes an activation region 121, bitline 122, word line 123, and accumulation capacitor 124. A registerpattern corresponding to each pattern is exposed by the opticalprojection exposure device (stepper) shown in FIG. 23. For thedeformation illumination of the exposure device, the 4 division lightsource shown in FIG. 33 is used. The deformation light source can beprovided, for example, in the following manner: a diaphragm 107 shown inFIG. 24 in which 4 holes are formed is disposed behind the fly eye lens101.

Only the pattern of the activation region 121 is a repeated pattern, andthis is also a chrome pattern of the photomask. This pattern 121 isobliquely extended on the drawing, and the deformation illumination 133is rotated and disposed so that a line to connect two elements locatedin the shortest distance among four elements 132 in the deformationillumination 133 can be parallel or vertical to the line direction ofthe pattern. In the case where the diaphragm 107 is used, only thediaphragm may be rotated. This is accomplished by adopting a case of thearrangement of the deformation illumination 132 shown in FIG. 28. Thismethod can be also applied to a case in which oblique patterns do notmake a right angle with each other as shown in FIG. 34(a). In this case,the deformation illumination 133 is rotated so that a line to connecttwo elements located in the shortest distance among four elements 132 inthe deformation illumination 133 can coincide with the center line ofthe direction in which two oblique patterns are extended. When thedeformation illumination is rotated, resolution improvement effect forthe patterns extending horizontally and vertically is decreased,however, in the activation region of DRAM shown in FIG. 30, thehorizontal and vertical patterns are disposed in a region except for acell. The pattern provided in a region except for the cell is designedto be larger than that provided in a hole portion. Therefore, even whenthe resolution improvement effect is decreased, no problems are caused.

The patterns of the bit line 122, word line 123 and accumulationcapacitor 124 are extended horizontally or vertically on the drawing.The bit line 122 is an approximately vertical line pattern, the wordline 123 is a horizontal line pattern, and the accumulation capacitor124 is a rectangular pattern, the longitudinal direction of which isvertical. In this case, the deformation illumination 133 shown in FIG.29 is disposed so that a line to connect two elements located in theshortest distance among four elements 132 in the deformationillumination 133 can be parallel or vertical to the direction of theline. When the disposition of the deformation illumination is changed,it can be rotated around the optical axis by angle 45° (see FIG. 34(b)).

In any cases, a pattern can be obtained under the following conditions:i rays (wavelength λ=0.365 μm) are used; a projection lens, thenumerical aperture (NA) of which is 0.5, is used; and the resolution ofline and space is 0.3 μm.

As explained above, according to the embodiment of the opticalprojection exposure method of deformation illumination system of thepresent invention, the optimal exposure is carried out in accordancewith the pattern profile so that a register pattern (a predetermineddevice pattern) of improved resolution can be provided.

FIG. 35 is a schematic illustration showing the structure of aprojection exposure device used for the projection exposure method ofthe present invention. In this drawing, numeral 201 is a disk-shapedlight source, numeral 202 is an optical axis, numeral 203 is adiaphragm, numeral 204 is an aperture, numeral 205 is a phase shiftmask, numeral 206 is a phase shifter, numeral 207 is a projection lenssystem, and numeral 208 is a surface to be exposed. In this projectionexposure device, exposure light having an optical intensity distributionof a primary direction is formed by using the diaphragm 203 having aplurality of apertures disposed below the disk-shaped light source 1being separated from the optical axis 202.

Exposure light transmitted through the aperture 204 of the diaphragm 203is irradiated on the shift mask (exposure mask) 205, and the exposurelight transmitted through the phase shift mask 205 is converged by theprojection lens system 207 and projected on the surface 208 to beexposed.

The projection exposure method of this embodiment is characterized inthe configuration of the optical intensity distribution on a section ofthe exposure light.

FIGS. 36(a) and 36(b) are schematic illustrations showing the structureof the diaphragm of the projection exposure device used for theprojection exposure method of the present invention.

Like parts are identified by the same reference character in each ofFIGS. 35, 36(a) and 36(b).

The diaphragm 203 shown in FIG. 36(a) is an example provided with theaperture 204 formed by the chords and arcs of one circle. The diaphragm203 shown in FIG. 36(b) is an example in which circular apertures 204are symmetrically formed on both sides of the optical axis.

A configuration of the optical intensity distribution on a section oflight transmitted through the diaphragm 203 having these apertures 204has a pattern that is wide in the direction of X (the primary direction)and narrow in the direction of Y (the direction perpendicular to theprimary direction).

As an example of the diaphragm of the projection exposure device of thepresent invention, FIGS. 36(a) and 36(b) are shown here. When theoptical intensity distribution of X direction (the primary direction)and that of Y direction are different on the section of exposure lighttransmitted through the apertures, the object of the present inventioncan be accomplished. Therefore, the aforementioned apertures may bereplaced with slit-shaped apertures, or a plurality of apertures may beprovided. Moreover, a plurality of oblique apertures forming anappropriate angle with respect to the aforementioned primary directionmay be provided.

When the exposure light, in which the optical intensity distribution ofX direction (the primary direction) on a section and that of Y directionare different from each other, is irradiated on a phase shift maskhaving a phase shift of 180°, the exposure light is transmitted througha portion close to the step portions of X and Y directions of the phaseshifter, and then converged by the projection lens system, so that theexposure light characteristics of the pattern projected on the surfaceto be exposed become non-symmetrical.

FIG. 37 is an optical intensity distribution diagram showing theintensity distribution of light transmitted through a phase shifter stepportion parallel with the primary direction.

The horizontal axis of this diagram shows a distance from the stepportion of the phase shifter of the phase shift mask, and the horizontalaxis shows the optical intensity of exposure light transmitted throughthe phase shift mask.

This diagram shows a result of calculation provided by a simulationconducted under the condition that the wavelength of exposure light is365 nm and the numerical aperture (NA) is 0.54. In the diagram, a solidline represents a case of just focus, and a broken line represents acase of 0.75 μm defocus.

In this case, incident angle θ of the light, which is sent from thedisk-shaped light source and incident on the phase shift mask throughthe diaphragm aperture, is determined by the following equation

θ=sin⁻¹(0.6 to 1.0)×(NA)×1/m

where NA: numerical aperture of the projection lens, and 1/m:magnification of reduction projection.

According to this diagram, in the case of just focus, and also in thecase of 0.75 μm defocus, the optical intensity of the exposure lighttransmitted through a portion close to a step portion of the phaseshifter of the phase shift mask is sharply lowered, so that a sharplinear unexposed portion having a very narrow width is formed all overthe thickness of a commonly used photoregister film, the thickness ofwhich is approximately 1 μm.

Consequently, when a positive type photoregister film is used, a minutelinear register pattern can be formed, and when this linear registerpattern is masked so that the film below the mask is etched and removed,a minute linear film can be formed.

On the contrary, when a negative type photoregister film is used, aregister pattern having a linear space can be formed. When this registerpattern having a linear space is masked so that the film below the maskis etched and removed, a film having a very minute linear space can beformed.

FIG. 38 is an optical intensity distribution diagram showing theintensity distribution of light transmitted through a phase shifter stepportion perpendicular to the primary direction.

The horizontal and vertical axes are the same as those shown in FIG. 37,and the exposure conditions are the same as those shown in FIG. 37.

According to this drawing, in the case of just focus, a sharp decreaseof optical intensity shown in FIG. 37 does not exist in a position closeto the step portion of the phase shifter of the phase shift mask. In thecase of 0.75 μm defocus, the optical intensity is increased to about1.0, however, an approximately flat optical intensity distribution canbe provided, and a linear unexposed portion is not formed.

When a positive type photoregister film is used, a register pattern isnot left after development. Therefore, when etching is conducted in themanner explained in FIG. 37, the film below the etched portion isremoved.

On the contrary, when a negative type photoregister film is used, aregister pattern having no openings can be formed, so that the lowerfilm can be prevented from being etched.

As can be seen in FIGS. 37 and 38, according to the present invention,the just focus characteristics and the defocus characteristicsexpressing the optical intensity distribution in the thickness directionof the register film are close to an ideal condition in which the effectof the present invention is clearly provided, and after the exposurelight has been transmitted through the phase shifter step portionperpendicular to the primary direction of the exposure light,interference of the exposure light is prevented.

As explained above, only when the sectional configuration of exposurelight is changed, an unnecessary unexposed portion generated in thephase shifter step portion can be removed by one exposure operationusing a sheet of phase-shift mask having no special structure such as amulti-step portion.

Embodiment 8

FIGS. 39(a) and 39(b) are schematic illustrations showing the projectionexposure method of the first embodiment.

FIG. 39(a) shows an exposure phase shift mask (reticule) used for theprojection exposure method of the first embodiment, and FIG. 39(b) showsa pattern formed by the projection exposure method of the embodiment 8.

In these drawings, numeral 211 is a shading film, numeral 212 is a 180°phase shifter, numeral 213 is a step portion of X direction, numeral 214is a step portion of Y direction, numeral 215 is exposure light, numeral216 is a linear pattern, and numeral 217 is a pad.

As explained in FIGS. 35 and 36(a)and 36(b), when the diaphragm 203having the aperture 204 is provided to the disk-shaped light source 201,the exposure light having an optical intensity distribution extending inthe primary direction (X direction) in a section is irradiated on thephase shift mask 205, and t he exposure light transmitted through thisphase shift mask 205 is converged by the projection lens system 207 onthe surface 208 to be exposed, so that a photoregister film coated onthis surface is exposed.

The phase shift mask (FIG. 39(a)) used for the projection exposuremethod of the first embodiment includes: a shading film 211corresponding to a pad, wherein the shading film 211 is provided on atransparent base plate; a step portion 213 of X direction parallel withthe primary direction (X direction) of the exposure light 215; and arectangular phase shifter 212 formed by a step portion 214 of Ydirection perpendicular to the step portion 213.

In the pattern (FIG. 39(b)) formed by the projection exposure method ofthe first embodiment shown in FIG. 39(a) in which the exposure light 215and the phase shift mask are utilized, a very narrow linear pattern 216is formed by the step portion 213 of X direction of the phase shifter212, and the exposure light transmitted through the step portion 214 ofY direction of the phase shifter 212 is directly sent to the primarydirection of the exposure light 215, so that the phases of exposurelight transmitted through this point do not coincide with each other andthe phase shift of 180° is not generated. Therefore, an unexposedportion is not formed, so that a linear pattern is not generated.

When the linear pattern 216 is formed from a conductive coat and apositive process is adopted, this embodiment can be applied to a case inwhich an isolated line portion is formed to be used as a minute gateelectrode in an integrated circuit using MOSFET is formed. Also, when anegative process is adopted, this embodiment can be applied to a case inwhich an opening portion such as a contact hole, is to be formed.

FIGS. 40(a) and 40(b) are schematic views for explaining the effectprovided by the first embodiment.

FIG. 40(a) is a schematic view of the tip portion (the left edge portionof FIG. 39(a)) of a pattern formed by a conventional disk-shaped lightsource, and FIG. 40(b) is a schematic view of the tip portion of apattern formed according to this embodiment.

The thickness of an etching register used for the formation of thepattern shown in the photograph was about 1 μm, and the width of thepattern register was about 0.15 μm. It can be seen that a minute patternwas formed all over the step portions of the phase shifter (X and Ydirections).

FIG. 40(b) shows a case in which exposure was carried out by exposurelight of which the primary direction was X. It can be seen that apattern including a sharp-unexposed portion was formed in the Xdirection, however, the pattern was not formed in the Y direction.

These photographs show an example of the positive process (process toprovide a line pattern of the register). Of course, when the negativeprocess is adopted, a space pattern can be provided.

In this embodiment, a rectangular phase shift has been explained thatwas formed from the step portion 213 of the X direction and the stepportion 214 of the Y direction perpendicular to the X direction on thebasis of the primary direction (X direction) of the exposure light 215.However, it is not always necessary that the step portions of the phaseshifter make a right angle with each other. For example, in the stepportions of a phase shifter that are crossed by an angle 45°, anunexposed portion can be effectively removed.

Embodiment 9

FIGS. 41(a) and 41(b) are schematic illustrations of the projectionexposure method of the embodiment.

FIG. 41(a) is a schematic illustration of a phase shift mask used forthe projection exposure method of the second embodiment, and FIG. 41(b)is a schematic illustration of a pattern formed by the projectionexposure method of the second embodiment.

In these drawings, numeral 221 is a shading film, numeral 222 is a 180°phase shifter, numeral 223 is a step portion of the X direction,numerals 224 and 225 are step portions oblique with respect to the Xdirection by an angle 45°, numeral 226 is a step portion of the Ydirection, numeral 227 is exposure light, numeral 228 is a linearpattern, and numeral 229 is a pad.

In this embodiment, a photoregister film is exposed with the exposuredevice explained in FIGS. 35 and 36 using the phase-shift mask.

FIG. 41(a) shows a portion of the phase-shift mask (reticule) used forthe projection exposure method of the second embodiment. On atransparent base plate, there are provided a shading film 221corresponding to a pad, step portion 223 of the X direction that is aprimary direction of exposure light 227, step portion 226 of the Ydirection, and a pentagonal phase shifter 222 formed by the two stepportions 224, 225 oblique to the upper edge of the step portion 226 ofthe Y direction by an angle 45°.

FIG. 41(b) shows a pattern formed by the projection exposure method ofthe second embodiment in which the exposure light 227 and thephase-shift mask shown in FIG. 41(a) are used. A minute linear pattern228 is formed by the step portion 223 of the X direction of the phaseshifter 222. Rays of light corresponding to the two step portions 224and 225 oblique to the step portion 223 of the X direction of the phaseshifter 222 cross the primary direction (the X direction) of theexposure light by an angle 45°, and a ray of light corresponding to thestep portion 226 of the Y direction crosses the primary direction of theexposure light by an angle 90°, so that a phase shift is not caused andthe linear pattern is not generated.

This embodiment can be applied to a case in which a gate electrode isformed in MOSFET by the positive process in the same manner as the firstembodiment.

Also, according to this embodiment, an aperture to come into contactwith source and drain regions can be formed by the negative process inwhich the phase shifter applied to the formation of gate electrodes isused.

An angle formed between a ray of exposure light incident on the exposuremask and the optical axis will be investigated here in each embodimentdescribed above.

When the angle θ formed between the exposure light incident on theexposure mask and the optical axis is small, it is natural in principlethat the effect to erase an unexposed portion generated by theunnecessary step portion of the shifter is reduced, and when the angle θis large, the effect to erase the exposure pattern of the unnecessarystep portion is large.

However, when θ is increased, the resolution of the exposure pattern isdeteriorated.

According to the experiments made by the inventors, the followingeffects have been observed:

When exposure light is used having an optical intensity distributionextending in a primary direction included in a range of θ with respectto the optical axis, even when the photoregister film is thick and theexposure amount is small, an unnecessary unexposed portion can beeffectively erased while the resolution is maintained high, wherein θ isdetermined by the following equation.

θ=sin⁻¹(0.4 to 1.0)×(NA)×1/m

NA: numerical aperture of the projection lens

1/m: magnification of reduction projection

On the assumption that the numerical aperture (NA) of the projectionlens is 0.54 and the magnification “m” of reduction projection is 5,this angle θ is expressed as follows: θ=sin⁻¹0.43 to sin⁻¹0.11, that is,θ is about 2° to 6°.

Embodiment 10

In each embodiment described above, a case is explained in which aminute linear pattern, for example, a gate electrode is formed by thestep portion of the phase shifter.

However, in the case where a phase shift mask (reticule) is formed byforming the phase shifter after the shading pattern corresponding to thepad has been formed from a shading film made of chrome on thetransparent base plate, there is a possibility that a positionalslippage is caused between a shading pattern formed before and a phaseshifter formed after.

Therefore, the following method can be considered:

A minute linear pattern is formed concurrently with other shadingpatterns, and a phase shifter is formed so that the step portion can bedisposed on this minute linear pattern. In this way, an unexposedpattern is formed by the minute linear pattern in an accurate positionalthough the unexposed pattern is not sharp. A sharp unexposed portionis formed by the step portion of the phase shifter. An accurateunexposed portion is formed at an accurate position by the unexposedportions of the two.

FIG. 42 is a schematic illustration of the projection exposure method ofthe embodiment 10.

This drawings shows a portion of the exposure mask (reticule). Numeral231 is a shading pattern corresponding to a pad, numeral 232 is a minutelinear shading pattern, numeral 233 is a phase shifter, numeral 234 is astep portion of the X direction, and numeral 235 is a step portion ofthe Y direction.

In this embodiment, the shading pattern 231 corresponding to a pad andthe minute linear shading pattern 232 are provided by a vapor-depositionfilm made of chrome and the like. On the shading pattern 231 and thelinear shading pattern 232, the phase shifter 233 is formed so that thestep portion 234 of the X direction can be disposed on the linearshading pattern 232.

According to this embodiment, even when the linear pattern 232, thedimensions of which are 0.2×(λ/NA)×m (the dimensions on the mask, λ:wavelength of exposure light) exists on the step portion 234 of the Xdirection of the phase shifter, no problems are caused in the generationof a sharp unexposed portion generated by the step portion 234 of hephase shifter 233. Accordingly, a positional slippage caused when thephase shifter 233 is formed can be allowed in the aforementionedallowable range.

Embodiment 11

When the diaphragm having an aperture disposed below the disk-shapedlight source is appropriately rotated so that the primary direction ofexposure light is changed in the projection exposure method of thepresent invention, another embodiment can be considered.

FIGS. 43(a) to 43(c) are schematic illustrations of the projectionexposure method of the embodiment 11.

FIG. 43(a) shows a phase shift mask provided with a rectangular phaseshifter. FIG. 43(b) shows a linear exposure pattern in the case wherethe primary direction of exposure light is in the X direction (thelateral direction in the drawing). FIG. 43(c) shows a linear exposurepattern in the case where the primary direction of exposure light isperpendicular to the X direction.

In this drawing, numeral 241 is a phase shifter, numeral 242 is anexposure pattern of the X direction, and numeral 243 is an exposurepattern of the Y direction.

In this embodiment, first, the exposure light, the primary direction ofwhich is X, is irradiated on the phase shift mask having a plurality ofrectangular phase shifters, so that a large number of linear patterns ofthe X direction composed of a sharp unexposed portion are formed by thestep portion of the X direction of the phase shifter on the surface tobe exposed.

After that, the primary direction of exposure light is rotated by anangle 90°, and another surface to be exposed is exposed with this phaseshift mask, so that a plurality of linear unexposed patterns of the Ydirection are formed by the step portion of the Y direction of the phaseshifter.

According to this embodiment, when a sheet of phase shift mask having aphase shifter is used, an unexposed portion pattern can be formedcorrespondingly to the configurations of the step portions of the phaseshifter of each direction that are perpendicular to each other.

In this embodiment, a rectangular phase shifter having the step portionsperpendicular to each other is explained. However, the same effect asthat of this embodiment can be provided when the phase shifter is formedinto an arbitrary polygon or a phase shifter surrounded by a curvehaving a gentle radius of curvature is formed and the exposure light isrotated by an angle in accordance with the configuration of the stepportion of the phase shifter.

The explanation of each embodiment described above is limited to a casein which a phase shift mask is used, however, the principle of thepresent invention can be applied to an exposure mask formed of a shadingfilm not having a phase shifter.

Embodiment 12

FIG. 44 is a schematic illustration of an exposure mask used for theprojection exposure method of the embodiment 12.

In this drawing, numeral 251 is a line and space shading pattern of theX direction, numeral 252 is a line and space pattern of the Y direction,and numeral 253 is exposure light.

In this embodiment, a photoregister film is exposed with the exposuredevice explained in FIGS. 35 and 36 using an exposure mask.

FIG. 44 shows a portion of the exposure mask (reticule) used for theprojection exposure method of the fifth embodiment. When the primarydirection of the exposure light 253 is defined as X, the line and spaceshading pattern 251 of the X direction and the line and space shadingpattern 252 of the Y direction perpendicular to the X direction areformed on a transparent base plate.

According to the projection exposure method of this embodiment, a lineand space exposure pattern of high resolution is formed on a surface tobe exposed by the line and space shading pattern 251 of the X direction.However, the resolution of a pattern formed by the line and spaceshading pattern 252 of the Y direction perpendicular to the X directionis not good, so that a pattern is generated by which half of theexposure light is shaded in total.

Consequently, when the amount of exposure and the progress ofdevelopment are adjusted, only the line and space photoregister patternof the X direction can be formed.

On the contrary to the above explanation, when the primary direction ofexposure light is Y, only the line and space photoregister pattern ofthe Y direction can be formed.

That is, when the diaphragm 203 having the aperture 204 disposed belowthe light source 201 shown in FIGS. 35 and 36(a)-(b) is rotated by 90°,two kinds of exposure patterns can be selectively formed using one sheetof exposure mask.

As explained above, an exposure pattern generated by the edge portion ofan unnecessary direction of the phase shifter can be removed withoutusing a plurality of masks or a multi-stage shifter, so that a highlyintegrated semiconductor device having a minute pattern can be easilymanufactured.

Embodiment 13

In order to meet the demand of forming minute patterns, in theconventional exposure technique of photolithography, a large convergencelens to converge a ray of light sent from a light source has been usedfor the purpose of improving the resolution.

However, when the lens size is increased, the focal depth is decreased,so that the accuracy of focal position necessarily becomes severe.Therefore, unless a focusing operation is properly conducted, resolvingpower is deteriorated even when the lens size is increased for improvingthe resolution.

In order to avoid these problems, for example, attention is given to anoblique incidence illumination method disclosed in official gazette ofJapanese Unexamined Patent Publication No. 2-142111 (1990).

According to the aforementioned method, a ray of light that isvertically incident on a lens is incident being oblique at apredetermined angle, so that focusing is conducted using interference oflight.

However, in the aforementioned conventional method, the same lightsource is used for any device patterns without giving attention to theprofile of the light source. Accordingly, the following problems arecaused.

Conventionally, in order to accurately conduct a focusing operation inoblique incidence illumination, the optical intensity distribution mustbe uniform. However, the spectral distributions of masks differ with theprofiles of the masks. For example, the spectral distribution of apattern shown in FIG. 53(a) is illustrated in FIG. 54(a), and thespectral distribution of a pattern shown in FIG. 53(b) is illustrated inFIG. 55(a). In this connection, in FIGS. 54(a)-(c) and 55(a)-(c) Frepresents a space coordinate of X-axis direction, and G represents aspace coordinate of Y-axis direction. FIGS. 54(b) and 54(c) respectivelyrepresent the sections of the X and Y directions in FIG. 54(a), and alsoFIGS. 55(b) and 55(c) represent the sections of the X and Y directionsin FIG. 55(a).

In order to sufficiently obtain the effect of oblique incidenceillumination, it is necessary to provide a light source profile capableof most excellently reproducing a device pattern. However, theoptimization method for a light source profile has not beenconventionally provided. For example, it is common to conductillumination with a light source through an aperture, the profile ofwhich is shown in FIG. 56.

The reason why the aforementioned light source has been conventionallyused will be described as follows:

Existence of a light source profile that can most excellently reproducea device pattern has been known. However, the profiles of actualpatterns are complicated so that it is difficult to theoretically findthe optimal light source profile such as a simple pattern (referred toas line and space, hereinafter) composed of simple lines disposed atregular intervals. Therefore, it has been actually impossible to findthe optimal light source profile for an actual pattern.

In FIGS. 57(a)-(f) and 58(a)-(f) pattern images are shown that can beobtained when two different types of patterns are irradiated by thelight source through an aperture shown in FIG. 56 while the focusingposition is being changed. In the drawing, FIG. 57(a) shows a patternimage in the case of DF=0, FIG. 57(b) shows a pattern image in the caseof DF=0.25, FIG. 57(c) shows a pattern image in the case of DF=0.5, FIG.57(d) shows a pattern image in the case of DF=0.75, FIG. 57(e) shows apattern image in the case of DF=1.0, FIG. 57(f) shows a pattern image inthe case of DF=1.25.

As can be seen in FIGS. 57(a)-(f) and 58(a)-(f) in the case of theconventional light source profile, when the DF value exceeds DF=0.5, theobtained pattern images are far different from the original image(DF=0). Therefore, the effect of oblique incidence can not besufficiently exerted under this condition.

In order to accomplish the optimization method for a light sourceprofile of the present invention, as shown in FIG. 45 in which theprinciple of the present invention is illustrated, the present inventionis to provide an optimization method for a light source profile in whichoptimization combination processing is conducted so as to calculate thelight source profile in the following manner: a light source surfacehaving a predetermined irradiation area is divided into predeterminedblocks; a point light source corresponding to each divided block isassumed to be a processing element of optimization processing; theprocessing element is made to be binary information; and a value of theprocessing element is varied by the number of the blocks in accordancewith the conditions of a device profile, mask profile, optical parameterand optimization parameter until a predetermined evaluation judgementcondition can be satisfied.

In this case, the following methods are effectively used for theoptimization combination processing: a simulated annealing method; and amethod in which the optimization combination processing is carried outin such a manner that: optical intensity is calculated for each pair ofpoint light sources symmetrical with respect to the optical axis; thepair of point light sources are successively adopted from the one, thefocal depth of which is largest, until a predetermined illumination canbe provided.

According to the present embodiment the optimization processing for alight source profile is conducted in an actual pattern by theoptimization combination processing until a predetermined evaluationjudgement condition is satisfied, so that the optimal light sourceprofile can be obtained in accordance with a device pattern.

That is, when the light source profile is optimized, the effect ofoblique incidence illumination can be fully exerted.

With reference to the drawings, the present embodiment will be explainedas follows.

FIG. 46 is a view showing an embodiment of the optimization method of alight source profile according to the present invention, and it is aflow chart showing an outline of the processing.

First, with reference to FIG. 46, an outline of the entire processingwill be explained.

First, in the present embodiment, a mask pattern profile to betransferred, a register pattern profile to be formed, conditions (NA, λ,and σ) of the optical system such as a stepper, and a threshold value tocalculate teaching data, are input (S1), and a sampling point (refer to“equation 1”) to evaluate a light source is generated on the wafersurface (S2).

X={x 1, x 2, . . . , x _(n)}

Next, ideal optical intensity data is registered as teaching data (referto “equation 2”) for each sampling point (S3).

K(X)={k(x 1), k(x 2), . . . , k(x _(n))}

Then, the light source surface having a predetermined illumination areais divided into elements for each predetermined block as a fly-eye lens,and a combination (refer to “equation 3”) is selected as a binaryelement of on and off (S4).

S=|s 1, s 2, . . . , s _(n)|

After the combination has been selected by means of element division,optical intensity distribution I(X) in the case of transfer of the maskis calculated, and evaluation function H of the light source is found(S5). In this connection, H(X, S) is calculated in the following manner:a difference between ideal optical intensity at each point of X andactual optical intensity is multiplied by a predetermined constant thatis a weight; and all calculated differences are added.

After processing S4 and processing S5 have been carried out, acombination S in which evaluation function becomes minimum is found, andprocessing is completed (S6).

In this embodiment, the simulated annealing method (referred to as an SAmethod, hereinafter), which is one of the combination optimizationmethods, is applied to the optimization processing for a light sourceprofile.

The SA method is defined as a method to which the Monte Carlo Method(Metropolis Method) is applied for solving the optimization problems. Itis not an algorithm to solve a specific problem, but it is a system toeffectively find an optimal solution.

In an optimization problem in which a solution is improved on the basisof an evaluation function, the conventional algorithm only conductsprocessing in a direction in which the evaluation function is improved.Therefore, once the solution has reached a local minimum value, anotherbetter solution can not be found even when it exists. However, in thecase of the SA method, under a certain condition, even when theevaluation function is deteriorated, the processing advances under thesame condition. Accordingly, there is a high possibility to find abetter solution that can not be obtained by the conventional algorithm.

That is, in the case of the SA method, a stochastic approach is adoptedfor the exchange of conditions. For that reason, relatively, theobtained solution is less susceptible to a local solution, and a stablesolution can be found irrespective of the initial condition.

Specifically, in the SA method, a cost function of the system is given,and a vector variable X is found so that the cost function can beminimum. In this case, X is assumed to be an arrangement of fly eyes,and cost function H(X) is determined by the grade of difference betweenan actual optical intensity distribution when X is in a certaincondition, and an ideal optical intensity distribution, and then thecalculation is conducted by the SA method so that cost function H(X) canbe reduced. In this manner, a fly eye arrangement closest to the idealoptical intensity distribution can be found.

The processing conducted by this SA method will be. explained byreference to FIG. 47.

In FIG. 47, the SA method is shown by an algorithm in which annealing ofmetal is adopted as a model. When temperature parameter T is given tothe system and annealing is gently conducted from a high temperature,the minimum energy condition is found.

That is, a property is given in which energy is either decreased orincreased when the temperature is high, and energy is only decreasedwhen the temperature is low. Then, the temperature is gently loweredfrom a high temperature condition. Under the aforementioned condition,when an equilibrium is found at each temperature, a condition in whichthe energy of the system can be minimized is given when the temperatureis sufficiently low.

In this case, energy is an evaluation function, and the evaluationfunction is obtained when a difference between actual and ideal valuesis multiplied by a weight. Therefore, in this case, high energyrepresents a bad condition, and the condition represents a combinationof light source profiles.

Accordingly, in this embodiment, when the present light source profileis S₀, the evaluation function is Ho, and the next light source profileis S₊, and the evaluation function is H₊. In accordance with a relationbetween evaluation functions H₀ and H₊, evaluation is conducted, so thata light source profile is found in which the minimum evaluation isprovided.

In FIG. 47, primary processing of this embodiment is shown.

First, evaluation function H₊ is found by the aforementioned processingS4 and processing S5, and a difference (refer to “equation 4”) betweenevaluation functions H₀ and H₊ is found (S11).

ΔH=H ₊ −H ₀

Next, temperature parameter T and uniform random numbers of 0<r<1 aredefined, and it is judged whether they satisfy “equation 5” or not(S12). In this case where they satisfy “equation 5”, evaluation functionH₊ is made to be H₀, and light source profile S₊ is made to be S₀, sothat the condition transits (S13).${\exp \left( {- \quad \frac{\Delta \quad H}{T}} \right)} > r$

When an equilibrium is attained in this condition, temperature parameterT is reduced (S 14, S 15), and then it is judged whether the temperatureis sufficiently low or not. When it has been judged that the temperatureis low, the processing is completed (S 16).

On the other hand, in the case where the equilibrium is not attained orthe temperature is still high, the program returns to the aforementionedS 11 and repeated.

The light source profile obtained by the aforementioned processing ismost effective for the mask profile. For example, for the pattern shownin FIGS. 50(a)-(f) which shows a conventional example, the light sourceprofile shown in FIG. 48 is obtained, and for the pattern shown in FIGS.51(a)-(f), which shows a conventional example, the light source profileshown in FIG. 49 is obtained.

FIGS. 50(a)-(f) shows a pattern image obtained when the same pattern asthat shown in FIGS. 57(a)-(f) is irradiated with the light source shownin FIG. 48. FIGS. 51(a)-(f) show a pattern image obtained hen the samepattern as that shown in FIGS. 58(a)-(f) is irradiated with the lightsource shown in FIG. 49.

As shown in FIGS. 50(a)-(f) and 51(a)-(f) a pattern image irradiatedwith the light source profile optimized by this embodiment is strong forfaithful defocus with respect to an original image (DF=0) in a widefocal position as compared with the conventional examples shown in FIGS.57(a)-(f) and 58(a)-(f).

FIG. 52 is a view showing another embodiment (Embodiment 14) of theoptimization method for a light source profile according to the presentinvention. It is a flow chart showing the primary processing.

In this embodiment, the following problems of the SA method shown inFIG. 47 are solved:

(1) It takes time to calculate.

(2) It is complicated and difficult to designate the parameters.

In the SA method, the profile of a light source is expressed in the formof combination of light source pixels, and the optimal combination isfound. In the case of a usual optical exposure device, image formationis attained by partial coherent light. Therefore, it can be consideredthat the images formed by light source pixels of each light source donot interfere with each other.

Accordingly, an approximate solution of the optimal light source can befound when the divided elements of the light source are selectedsymmetrically with respect to the optical axis, each pair of lightsources are evaluated, and light sources, the number of which isappropriate for providing illumination necessary for exposure, areadopted.

That is, in this embodiment, a pair of light sources symmetrical withrespect to the optical axis are defined as a unit, and each opticalintensity distribution is found, and then pairs of light sources areadopted until a predetermined illumination can be provided, wherein theadoption is made in the order of strength against defocus such that apair of light sources stronger against defocus are adopted first.

In this case, whether or not a pair of light sources are strong againstdefocus is judged by collapse of a pattern in simulation.

In accordance with FIG. 52, the procedure will be explained as follows.

First, evaluation function H is found by processes S4 and S5 describedabove. Processing (S 21) to store this evaluation function H isconducted on all the light sources (S 22).

In accordance with stored data for each light source, light sources areadopted in the following manner: a light source that is strongestagainst defocus and forms an optical intensity distribution closest toteaching data distribution is adopted first; and then light sources aresuccessively adopted until the illumination becomes a value σ (S 23).

According to the above processing, the optimal light source profile canbe effectively found, so that the calculation time can be greatlyreduced as compared with the example according to the aforementioned SAmethod.

As a result, a profile that can be easily realized is obtained. When alight source suitable for a pattern profile is used, the resolution andfocal depth can be improved. As explained above, according to thisembodiment, the optimization of a light source profile for an actualpattern, which has been conventionally assumed to be difficult, can berealized by means of the optimization combination processing, so thatthe optimal light source pattern can be provided in accordance with adevice pattern.

Consequently, the effect of oblique incidence illumination can beeffectively exerted, and the invention can contribute to improvement inphotolithographic technology.

According to the present embodiment, the optimization of a light sourceprofile for an actual pattern, which has been conventionally assumed tobe difficult, can be realized by means of the optimization combinationprocessing in which the optimization is conducted until a predeterminedevaluation judgement condition is satisfied. Therefore, the opticallight source pattern can be provided in accordance with a devicepattern.

Accordingly, the effect of oblique incidence illumination can besufficiently exerted, and the accuracy of precise processing ofphotolithography can be improved.

Embodiment 15

Before the embodiment 15 of the present invention is explained, exposuretechnique such as phase shift mask and oblique incidence illuminationwill be explained in which the phase difference is used.

FIG. 63(a) is schematic of a phase shift mask. A shading metallic film323 made of chrome is selectively provided on the surface of atransparent base plate 322 made of quartz, so that apertures aredetermined. In one of the adjoining apertures, a phase shifter 324 madeof a SiO₂ film is formed.

Thickness of the phase shifter 324 is selected so that the phase oflight passing through the phase shifter can be delayed with respect tothe phase of light passing through an aperture having no phase shifter.For example, the thickness of the phase shifter 324 is selected so thata phase difference of half wavelength can be generated.

Consequently, concerning rays of light 321 a and 321 b that have passedthrough the adjoining aperture, a phase of the ray of light 321 a thathas passed through the aperture having no phase shifter advances by ahalf wavelength as compared with a phase of the ray of light 321 b thathas passed through the aperture having a phase shifter. Theaforementioned waves of reverse phase are canceled with each other wheninterference is caused, so that the optical intensity is reduced.

FIG. 63(b) is a schematic illustration for explaining oblique incidenceillumination. The shading metallic film 323 made of chrome isselectively provided on the surface of the transparent base plate 322made of quartz so that adjoining apertures are determined.

Rays of light 321 a and 321 b are irradiated to the adjoining aperturesin an oblique direction. Study is made at a point of time when the raysof light have passed through the mask. Since the ray of light 321 b haspassed through a longer optical path than that of the ray of light 321a, the phase of the ray of light 321 b is delayed as compared with thatof the ray of light 321 a. In the case where the phase difference isselected to be a half wavelength, the optical intensity is reduced wheninterference is caused between these two rays of light in the centers ofthe two apertures and on the normal line of the base plate.

FIG. 63(c) is a schematic illustration showing a change of the amplitudeof light in the case where the two rays of light of reverse phaseinterfere with each other. When a ray of light having an amplitude shownby curve “a” interferes with a ray of light of reverse phase shown bycurve “b”, an amplitude of light shown by curve “c” can be obtained. Inthis case, in a region where the two rays of light are superimposed, theamplitude is reduced because the phases of the rays of light are reverseto each other.

FIG. 63(d) shows an optical intensity distribution in the case where theaforementioned interference has occurred. Rays of light of reverse phasethat have been spread by diffraction, are superimposed in the endportions between the rays, so that the amplitude is reduced.Accordingly, the optical intensity is also reduced. As described above,when two rays of light having a phase difference interfere with eachother, the width of distribution of light that has been spread bydiffraction can be restricted.

FIG. 64 is a schematic illustration for explaining the function of aphase shift mask,. Rays of light 325 and 326 are incident on the maskand emergent from the phase shifter. A phase difference corresponding toa half wavelength is caused between the emergent rays of light 325 c and326 c, for example, the ray of light 326 c has a phase differencecorresponding to a half wavelength with respect to another ray of light325 c. The intensity of light of reverse phase is reduced in accordancewith the amplitude when interference is caused.

In order to form an image on a projection surface, it is necessary thatat least two rays of diffraction light 325 a and 326 a (or 325 b and 326b) of the −1 order generated from two rays of light 325 and 326,interfere with two rays of diffraction light of the first order on theprojection surface.

A direction in which diffraction light of the −1 order is generated withrespect to pitch “p” of two rays of light 325 and 326 is studied here.An optical path difference between the rays of light 326 a and 325 a isp·sin θ as shown on the right of FIG. 64(a). With respect to diffractionlight of the −1 order, the optical path difference is the same.

When pitch “p” is large, diffraction light of multi-order is incident onthe projection lens, however, as pitch “p” is decreased, the number ofthe order of the light incident on the projection lens is lowered.Consequently, in the case where a high resolution is required, behaviorsof rays of light of the 0 and first orders are important.

In the phase shift mask, a phase shifter is formed in one of theadjoining apertures, so that the phase of emergent light is different byangle π. Consequently, diffraction light of the ±1 order is generated ina direction in which p·sin θ becomes equal to π. Angle θ in whichdiffraction light of the first order is generated becomes larger aspitch “p” is reduced.

FIG. 64(b) is schematic of an image formation system in the case wherethe aforementioned phase shift mask is used.

A ray of light sent from a light source is projected onto a phase shiftmask 332 through a condenser lens 331. At this time, a central ray oflight 334 of the luminous flux is irradiated vertically to the phaseshift mask 332.

The ray of light that has passed through the phase shift mask 332becomes two luminous fluxes of opposite phase, and the ray of light 335of the 0 order that advances straight is canceled by interference. Whenthe optical intensities of both luminous fluxes are approximately thesame, the entire optical intensity is approximately extinguished, sothat the ray of light is mainly composed of the ray of light 336 of the−1 order and the ray of light 337 of the first order. When the two raysof light 336 and 337 are irradiated on the projection surface with theprojection lens 333, an image is formed.

FIGS. 65(a) and 65(b) are schematic illustrations for explaining obliqueincidence illumination exposure. FIG. 65(a) is schematic of a behaviorof light in oblique incidence illumination exposure. A diaphragm plate340 having an aperture portion divided into two is disposed below thecondenser lens 341.

A ray of light incident on the condenser lens 341 passes through theaperture of the diaphragm plate 340, and only the light that has passedthrough the aperture is projected onto the mask 342. Therefore, the rayof light 344 incident on the mask 342 is oblique to the mask 342 byangle θ.

When the ray of light oblique to a normal line is incident on theadjoining apertures as described above, a phase difference is causedbetween the adjoining apertures as explained in relation to FIG. 63(b).A ray of light advancing in a direction of the normal line of the baseplate is canceled by interference, and as diffraction light, a ray light345 of the 0 order that advances straight, a ray of light 346 of the −1order and a ray of light 347 of the first order are generated. Under thecondition shown in the drawing, the ray of light 345 of the 0 order andthe ray of light 347 of the first order are collected by the projectionlens 343 and irradiated onto the projection surface.

As pitch “p” between the adjoining apertures on the mask 342 is reduced,an angle formed between the ray of light 345 of the 0 order and the rayof light 347 of the first order is increased. Therefore, in order tocollect these rays of light, it is necessary to use a projection lens343 having a large numerical aperture.

FIG. 65(b) is a schematic illustration for explaining an optical systemof oblique incidence illumination exposure.

A condenser lens 341, mask 342 and production lens 343 are disposed onthe optical axis. An angle formed between a ray of light obliquelyincident on the mask 342 from the condenser lens 341 and the opticalaxis is represented by angle θ₁. An angle formed between a ray of lightemitted from the mask 342 that passes through the outermost portion ofthe projection lens 343 and the optical axis, is represented by angleθ₂.

An angle formed between the optical axis and a ray of light that haspassed through the outermost portion of the projection lens 343 andadvances on the projection surface, is represented by angle θ₃.

where

σ=sin θ₁/sin θ₂

sin θ₂=NA/m

NA=sin θ₃

In this case, NA is a numerical aperture, and 1/m is a reduction ratio.

At this time, the following equation is satisfied.

sin θ₁=σ·sin θ₂=σ·(NA/m)

The above equation can be rewritten as follows.

θ₁=sin⁻¹{σ·(NA/m)}

The maximum angle of angle θ₁ formed by a ray of light incident on themask 342 is expressed as follows.

θ₁=θ₂

In this case, σ=1.

In the case of oblique incidence illumination exposure, a ray of lightadvancing along the optical axis is the cause of deterioration of theresolution. Therefore, it is desired to increase angle θ₁ of incidentlight to a certain extent.

For example, it is desirable that the following inequality is satisfied.

0.4≦σ≦1

FIGS. 66(a) and 66(b) are schematic illustrations for explaining adifference of image forming ability caused by polarization. In thiscase, a parallel pattern of line and space is formed on the mask.

FIG. 66(a) is a view for explaining a case in which polarized lightparallel with a pattern direction of line and space is used for imageformation.

Assume that a pattern of line and space is formed on the mask 307 in adirection vertical to the surface of the drawing. Assume the linearlypolarized light which has been polarized in a direction vertical to thesurface of the drawing is vertically incident on the mask 307. That is,the direction of polarization and that of the pattern are parallel witheach other.

After the ray of light has passed through the mask 307, diffractionlight 315 of the −1 order and diffraction light 316 of the first orderare generated as shown in the drawing, and collected by the projectionlens 308, and the collected light is incident on an exposure surfacesuch as a wafer 309. At this time, the direction of polarization isalways vertical to the surface of the drawing, and the direction ofpolarization of diffraction light 315 of the −1 order and that ofdiffraction light 316 of the first order are the same. Accordingly,diffraction light 315 of the −1 order and diffraction light 316 of thefirst order interfere with each other on the wafer 309, and an image isformed.

FIG. 66(b) shows a behavior of light in the case where the direction ofline and space pattern is vertical to the direction of polarization. Inthe same manner as a case shown in FIG. 66(a), the mask 307 is providedwith a line and space pattern in a direction vertical to the surface ofthe drawing. Linearly polarized light having the polarization directionof the surface of the drawing. is vertically incident on the mask 307.

The polarization direction of diffraction light 315 of the −1 order andthat of diffraction light 316 of the first order are on the surface ofthe drawing after the light has passed through the mask 307, and thepolarization direction is vertical to the advancing direction of light.The polarization direction of light collected by the projection lens 308and irradiated on the wafer 309 is also vertical to the advancingdirection of light and on the surface of the drawing.

As can be seen from the drawing, when an angle formed betweendiffraction light 315 of the −1 order and diffraction light 316 of thefirst order is increased, the polarization directions cross each other,so that the degree of interference between diffraction light 315 of the−1 order and diffraction light 316 of the first order is reduced.

If diffraction light 315 of the −1 order and diffraction light 316 ofthe first order make a right angle with each other, interference is notcaused at all. That is, these two rays of diffraction light form noimage and become noise components.

According to the study described above, the present embodiment providesan exposure method in which only rays of light are used that caneffectively cause interference on the image forming surface.

FIG. 59 is a schematic illustration for explaining an exposure methodaccording to the embodiment 15 of the present invention. Numeral 301 is,for example, an extra-high voltage mercury lamp. A reflecting mirror 302is disposed above the light source 301, so that the light emitted upwardis reflected downward.

A fly eye lens is disposed below the light source 301 so that theincident light is uniformly irradiated on a mask 307. A polarizing plate304 is disposed between the fly eye lens 303 and the mask 307. Thepolarizing plate 304 is provided with a sufficient polarizing capacityfor a wavelength of light to be used.

The mask 307 is composed, for example, in such a manner that a phaseshifter is provided on a quartz glass plate. In this case, a region inwhich the optical intensity is reduced by interference is generatedalong the periphery of the phase shifter. Moreover, a chromic film todetermine an aperture through which light is transmitted may be formed.In this connection, a projection lens 308 is disposed below the mask307, and focuses the incident light on the wafer 309.

As shown in the drawing, a pattern in which a profile long in the Ydirection is repeatedly formed is provided on the mask 307. In thiscase, polarization direction P of the polarizing plate 304 is set in theY direction so that it can be parallel with the pattern direction on themask 307. Consequently, a ray of light that has passed through thepolarizing plate 304 is polarized in the Y direction as shown in thedrawing.

Diffraction light is generated in the light that has passed through thepattern on the mask 307, and the diffraction light is collected by theprojection lens 308 and focused on the wafer 309. At this time, thepolarizing direction of the light incident on the wafer 309 is orientedin the Y direction, so that the light effectively interferes with eachother, and an image is formed on the wafer 309.

FIG. 60 shows a sample pattern of a mask used for an experiment ofprojection exposure to which polarization is applied. The mask patternis composed of a line and space pattern 312 long in the Y direction, anda line and space pattern 314 long in the X direction. In this case, thepatterns 312 and 314 were made of only a phase shifter of SiO₂ providedon a quartz glass plate.

The optical conditions of the exposure system were as follows: exposurewavelength=365 nm (i ray), NA=0.54, and σ=0.5. Reduction ratio 1/m wasset at 1/5, and a plurality of mask patterns of different pitch weremade.

The film thickness of a phase shifter to form the patterns 312 and 314was about 388 nm. That is, when a ray of light passes through the phaseshifter, phase difference of π is caused in the light, the wavelength ofwhich is 365 nm.

For the photoregister, a PF115 material (brand name) manufactured bySumitomo Chemical Co., was used.

FIG. 61(a) is a schematic view of a register pattern obtained when asample pattern was exposed with non-polarized light according toconventional technique.

FIG. 61(b) is a schematic view of a register pattern obtained when asample pattern was exposed with polarized light in the Y direction.

According to the result of image formation of the pattern in which thephase shifters of 2 μm width on the mask (0.4 μm width on the wafer)were disposed at pitch of 4 μm, sufficient resolution was not providedby the conventional technique irrespective of the pattern direction.

On the other hand, as shown in FIG. 61(b), in the exposure in whichpolarized light in the Y direction was used, sufficient resolution wasprovided to the pattern that is long in the Y direction. However, theresolution of the pattern 314 that is long in the X direction is lowerthan that of the conventional technique.

As can be seen from the results shown in FIGS. 61(a) and 61(b), when thepolarizing direction is selected in accordance with the patterndirection, the resolution can be improved.

Accordingly, in the case where a pattern to be exposed is oriented inone direction, high resolution can be provided when linearly polarizedlight in the pattern direction is used. For example, it can be appliedto the exposure of an electrode of an SAW filter and also applied to theexposure of a diffraction grating.

When a pattern of the X direction and that of the Y direction are mixedin a pattern to be exposed, the pattern to be exposed is divided intotwo, and one of them may be selected in accordance with the polarizeddirection.

FIG. 62 is a view for explaining projection exposure of the embodiment16 of the present invention. For this embodiment, oblique incidenceillumination exposure is used. A light source 301, reflecting mirror302, fly eye lens 303, mask 307, projection lens 308 and wafer 309 arethe same as those explained in the embodiment shown in FIG. 59.

Between the fly eye lens 303 and the mask 307, is provided a diaphragmplate 305 having apertures disposed symmetrically with respect to anoptical axis. The diaphragm plate 305 is made of, for example, analuminum plate. A polarizing plate 306 is disposed in the aperture ofthe diaphragm plate 305. Accordingly, a ray of light emitted from thelight source 301 passes through the fly eye lens 303 and is transmittedthrough the polarizing plate 306 in the aperture of the diaphragm plate306, and then the ray of light reaches the mask 307.

In the case where the pattern on the mask 307 is long in the Ydirection, the apertures of the diaphragm plate 305 that are opposed toeach other are arranged in the X direction, so that the polarizingdirection of the polarizing plate is set in the Y direction. As a resultof the foregoing, the ray of light that has passed through the mask 307having the pattern of the Y direction reaches an image formation surfacewhile the polarizing direction is maintained in the Y direction, andimage formation is effectively conducted.

It is preferable that an oblique incidence angle θ₁ of a ray of lightincident on the mask is in the following range.

θ₁=sin⁻¹{(0.4 to 1.0)×(NA/m)}

The present invention has been explained above with reference to theembodiments, however, it should be understood that the present inventionis not limited to the specific embodiments. For example, in thestructure shown in FIG. 62, the diaphragm plate 305 and the polarizingplate 306 may be separate bodies. Moreover, the profile of the opposedapertures may be formed rectangular or into other shapes.

Moreover, it is possible to provide the mask with polarization effects.It will be clear for a person with ordinary skill in the art thatvariations, improvements and combinations can be made in the presentinvention.

When projection exposure is conducted with linearly polarized light thatis oriented in the mask direction, the resolution can be improved.

What is claimed is:
 1. A manufacturing method of semiconductor devicescomprising the steps of: irradiating a phase shift exposure mask havinga phase shifter with an exposure light having an optical intensitydistribution extending in a primary direction in its section; andprojecting the light transmitted through said phase shift exposure maskon a surface to be exposed; wherein an exposure is carried out on saidsurface with non-symmetrical exposure characteristics including onedirection which is substantially parallel to said primary direction, inwhich an unexposed portion having a sharp decrease of optical intensityis generated close to and along with an edge portion of the phaseshifter of said phase shift exposure mask, and also including a seconddirection, different from said first direction, in which the unexposedportion is not formed; and wherein an aperture such as a contact hole isformed through a negative process and an isolated line portion to beused as a gate electrode or a wiring layer is formed through a positiveprocess.
 2. The semiconductor devices manufacturing method according toclaim 1, wherein said phase shifter has a step portion including alinear shading portion, the width of which is not more than 0.2×(λ/NA)×m(λ: wavelength of exposure light, NA: numerical aperture of theprojection lens, m: magnification of reduction projection).